1. Field of the Invention
The present invention relates to a light-receiving module of a heat-resistant, vibration-resistant type for use in petroleum exploration and a radiation detecting apparatus equipped with the same.
2. Related Background Art
The petroleum exploration is commonly carried out, as shown in FIG. 1, with a probe 94, which comprises a radiation source 90 and a radiation detecting apparatus 92 mounted therein, by lowering into a drilled or drilling well bore 96 and operated to measure and analyze scattered rays or a level of natural radiation derived from a stratum 98. The radiation detecting apparatus 92 for use in the petroleum exploration is operated under hostile conditions with a higher temperature (150 to 200xc2x0 C.) and an unfavorable degree of vibration in such an oil well drilled deeply under the ground or in a drilling module for the petroleum drilling.
Such conventional radiation detecting apparatuses however have a drawback that its accuracy for detecting the radiation may decline during its operation.
The present inventors have investigated causes of declination in the accuracy of the radiation detection during the operation of the conventional radiation detecting apparatuses. It was then found that one of the causes was displacement of a photomultiplier installed in the radiation detecting apparatus which had been triggered by external environmental events.
It is thus an object of the present invention to provide a light-receiving module having an improved structure for effectively minimizing declination in the detecting accuracy during the operation and a radiation detecting apparatus equipped with the light-receiving module.
The light-receiving module according to the present invention comprises a photomultiplier having a faceplate and a stem opposing each other, a bleeder circuit board provided so as to sandwich the stem together with the faceplate and electrically connected to the photomultiplier, a module case provided so as to accommodate the photomultiplier and the bleeder circuit board, the module case having an opening for exposing the faceplate of the photomultiplier, a step provided on an inner surface of the module case, and a stopper seated on the step, defining the position of the photomultiplier in the module case. The light-receiving module allows the stopper seated on the step to define the position of the photomultiplier in the module case.
The step provided on the inner surface of the module case may preferably function as the stopper. As a result, the step can function as the stopper, thus reducing the number of the required components.
The stopper may also have a contact surface in contact with the stem of the photomultiplier, and a projection may be formed on the contact surface. Since the stem of the photomultiplier is in contact with the contact surface of the stopper, the position of the photomultiplier along a direction vertical to the faceplate can favorably be defined. Also, as its side wall is in contact with the projection provided on the contact surface, the photomultiplier can precisely be positioned along a direction parallel with the faceplate.
The stopper may also have a contact surface in contact with the stem of the photomultiplier, the contact surface being tilted with respect to a center axis of the module case. Accordingly, inclination of the faceplate of the photomultiplier to the opening of the module case can favorably be determined by controlling the position of the stem directly on the contact surface of the stopper.
Also, the stopper may be made of one of polyamide-imide resin and polyimide resin. This allows the stopper to be enhanced in the heat resistance, the physical strength and the electric non-condactance.
Preferably, a space in the module case where the bleeder circuit board is accommodated is filled with a potting compound. This will protect and hold the bleeder circuit board at its position in the module case.
More preferably, a space between the side wall of the photomultiplier and the module case may also be filled with a potting compound. This will prevent displacement of the photomultiplier in the module case.
A radiation detecting apparatus according to the present invention comprises a scintillator for converting incident radiation into light, a light-receiving module described above, having the faceplate in direct contact with the scintillator, a housing for accommodating the scintillator and the light-receiving module, and means for pressing the light-receiving module against the scintillator. In the present radiation detecting apparatus, the light-receiving module is pressed against the scintillator in a state that the faceplate is in contact with the scintillator. Accordingly, the photomultiplier can correctly be positioned between the scintillator and the stopper, hence ensuring the coupling between the light-receiving module and the scintillator under hostile conditions of a higher temperature and an unfavorable degree of vibration.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.